Light accelerates the splicing of srh1 homologue gene transcripts in aerial mycelia of Trichoderma viride

The expression of the Tvsrh1 gene encoding conidial hydrophobin was investigated during the development of surface- cultivated Trichoderma viride mycelia under different illumination regimes. Three transcripts of the whole gene amplified from the total mRNA were found with lengths of 400, 323 and 272bp. The 400-bp transcript was slowly converted to the shorter forms in the dark. Light-pulse dramatically increased the rate of conversion, and a permanent illumination of mycelia was most efficient in this process. The sequencing of transcripts revealed that the 400 bp transcript contains two introns, whereas the intermediate one contains only one intron located distally from the 5'-end. The shortest transcript was without introns. The sum of all transcripts remained almost unchanged in the dark and increased upon the light pulse but decreased during development under permanent illumination. The appearance of conidia coincided with the complete conversion of the transcripts. The results showed that the splicing of the two introns was not random but sequential, and that it did not follow the cotranscriptional mechanism. Furthermore, they suggested that mRNA processing could represent another regulation level of gene expression by light during the photoinduced conidiation in T. viride.